In addition to their structural roles in maintaining tissue integrity, the macro-molecules of the extracellular matrix have been implicated in influencing the course of developmental events in many tissues. Of specific interest to this proposal is the glycosaminoglycan, hyaluronate, high levels of which have been correlated with cell proliferation and migration; whereas, its removal by hyaluronidase has been associated with the cessation of these latter activities and the onset of overt differentiation. Despite the many correlative studies both in developing and remodeling tissues, neither the mechanism by which hyaluronate. Affects cell behavior nor the manner in which cells regulate hyaluronate levels are well understood. In this grant application, I propose first to define the cellular mode of action of hyaluronidase on hyaluronate substrate, and then to show how resultant alterations in hyaluronate levels affect specific aspects of cell behavior. To reach these objectives, three experimental approaches will be taken: (1.) Using chick embryo fibroblasts as an experimental model, present studies on the mechanism of hyaluronidase action will be expanded to include the subcellular localization of enzyme and substrate, the effects of lysosomotropic agents on hyaluronidase and hyaluronate levels, as well as enzyme feeding experiments; (2.) Preparation of specific antibodies to hyaluronidase for immunochemical and biosynthetic analyses to determine the pathway of enzyme processing and the nature of possible precursor forms of the enzyme; and (3.) biological studies in which data obtained from the preceding studies will be applied to two developmental systems in order to demonstrate how fluctuations in hyaluronate levels, at least in part under the metabolic regulation of hyaluronidase, affect cell behavior. These studies have direct bearing on furthering our understanding of the changes that occur during differentiation of skeletal muscle and during the formation of heart valve and septal tissue.